1. Field of the Invention
This invention relates to media such as recording medium, electrode substrate, etc., processes for producing these, recording device, the reproducing device which perform recording, reproducing with a probe electrode by use of such recording media, information processing devices including recording reproducing devices, and information processing methods including recording method, recording-reproducing method, recording-reproducing erasing method.
2. Related Background Art
In recent years, use of memory materials is at the center of electronics industries such as computers and their related instruments, video disc, digital audio disc, etc., and developments of such materials have been progressed extremely actively. The performances demanded for memory materials depend on the uses, but may generally include:
(1) high density and large recording capacity;
(2) rapid response speed of recording and reproducing;
(3) small consumption power;
(4) high productivity and low cost, etc.
Up to date, there have been semiconductor memory and magnetic memory utilizing magnetic materials or semiconductors as the base material, but with the progress of laser techniques in recent years, inexpensive and high density recording media by optical memory with the use of organic thin films such as of organic dyes, photopolymers, etc., have been launched in the field.
On the other hand, recently, a scanning tunnel microscope (hereinafter abbreviated as STM) which can directly observe the electron structure of the surface atoms of a conductor has been developed (G. Binnig et al., Phys. Rev. Lett., 49, 57 (1982)), and it has become possible to perform measurement of real space images with high resolving power regardless of whether they may be single crystals or amorphous, and still having the advantage that observation is possible at low power without causing a damage with current to the sample. Further, it can be actuated in the air and used for various materials, and therefore a wide range of applications have been expected therefor.
STM utilizes the phenomenon that a tunnel current flows when a probe of a metal (probe electrode) and an electroconductive substance are approached to a distance of about 1 nm with a voltage applied therebetween. Such current is very sensitive to the distance change between the two. By scanning the probe so as to constantly maintain the tunnel current, various information concerning the whole electronic cloud in the real space can be read. In this case, the resolving power in the interplanar direction is about 0.1 nm.
Therefore, by applying the principle of STM, it is possible to perform high density recording and reproducing sufficiently at atomic order (sub-nanometer). For example, in the recording and reproducing device disclosed in Japanese Laid-open Patent Publication No. 61-80536, the atomic particles adsorbed onto the medium surface are removed by electron beam, etc., writing is effected and the data are reproduced by STM.
There has been proposed the method of performing recording and reproducing by STM with the use of a thin film layer of a material having the memory effect of the switching characteristics of voltage and current, such as .pi. electron type organic compound or a chalcogenide compound (Japanese Laid-open Patent Applications Nos. 63-161552, 63-161553). According to this method, if the bit size of recording is made 10 nm, high capacity recording and reproducing as much as 10.sup.12 bit/cm.sup.2 are possible.
FIG. 7 shows a constitutional example of the information processing device in which STM is applied. In the following, description is made by referring to the Figure.
101 is a substrate, 102 an electrode layer of a metal, and 103 a recording layer. 201 is an XY stage, 202 a probe electrode, 203 a support for the probe electrode, 204 a Z-axis linear actuator for driving the probe electrode in the Z direction, 205, 206 are linear actuators for driving the XY stage in the directions X, Y, respectively and 207 is a pulse voltage circuit.
301 is an amplifier for detecting the tunnel current flowing from the probe electrode 202 through the recording layer 103 to the electrode layer 102. 302 is a logarithmic reducer for converting the change in tunnel current to a value proportional to the gap distance between the probe electrode 202 and the recording layer 103, 303 a low region passing filter for extraction of the surface unevenness component of the recording layer 103. 304 is an error amplifier for detecting the error between the reference voltage V.sub.REF and the output from the low region passing filter 303, 305 a driver for driving the Z-axis linear actuator 204. 306 is a driving circuit for performing positional control of the XY stage 201. 307 is a high region passing filter for separating the data component.
FIG. 8A shows a sectional view of the recording medium of the prior art example and the tip of the probe electrode 202.
401 is the data bit recorded on the recording layer 103, and 402 is the crystal grain when the electrode layer 102 is formed on the substrate 101. The size of the crystal grain 402 is about 30 to 50 nm by use of conventional vacuum vapor deposition method, sputtering method, etc. as the preparation method of the electrode layer 102.
The gap between the probe electrode 202 and the recording layer 103 can be kept constant by the circuit constitution shown in FIG. 7. More specifically, by detecting the tunnel current flowing between the probe electrode 202 and the recording layer 103, and the value after passing the current through the logarithmic reducer 302 and low region passing filter 303 is compared with the reference voltage, and by controlling the Z-axis linear actuator 204 supporting the probe electrode 202 so that the comparative value approaches zero, the gap between the probe electrode 202 and the recording layer 103 can be made substantially constant.
Further, by driving the XY stage 201, whereby the surface of the recording medium is traced with the probe electrode 202, and the high region frequency component of the signal at the &acirc ; point in FIG. 7 to enable detection of the data in the recording layer 103.
FIG. 9A shows the signal intensity spectrum for the frequency of the signal at the &acirc ; point at this time.
The signals of the frequency components of f.sub.o or less are due to gentle undulation of the medium on account of warping, distortion, etc. of the substrate 101. This signal with f.sub.1 as the center is due to unevenness of the surface of the recording layer 103, primarily on account of the crystal grain 402 formed during formation of the electrode material. f.sub.2 is the conveying wave component of the recording data, and 403 the data signal band. f.sub.3 is the signal component formed from the atomic, molecular arrangement in the recording layer 103.
When the recording medium shown in the prior art example was used, the following problems were involved.
For performing high density recording by making available high resolving power, which is the specific feature of STM, the data signal band 403 must be placed between f.sub.1 and f.sub.3. In this case, for separating the data components, a high region passing filter 307 in FIG. 7 with a shielding frequency f.sub.c is employed. However, the tail portion of the signal component of f.sub.1 overlaps the data signal band 403. This is because the signal component of f.sub.1 is caused by the crystal grain 402 in the electrode layer 102, and the recording size and the bit interval of the data are approximately 1 to 10 nm as compared with the crystal grain 402 of 30 to 50 nm.
For this reason, when high recording and reproducing is conducted, S/N ratio of recording reproducing is lowered to make the error ratio of reading data markedly high.
FIG. 8B shows a sectional view of the recording medium having a track and the tip of the probe electrode 202. 104 is a track.
In FIG. 9B, f.sub.T is a tracking signal. Although not shown in the information processing device in FIG. 7, the tracking signal f.sub.T is a signal which makes it possible for the probe electrode 202 to monitor the data series, which is realized by forming a step difference on the medium or writing a signal which can be detected when it comes off from the track.
In the case of using the recording medium shown in the prior art example, the following problem was involved.
The tracking signal f.sub.T can be placed only in the vicinity of f.sub.o. For this reason, the tracking signal f.sub.T will have a frequency considerably lower as compared with the data signal band 403, whereby the data monitoring will be lowered. This results in increased reading error ratio of the data, thus posing a problem that reliability during information processing is lowered.